u-boot: select $fdt_file basing on $board_id (if defined)

Carrier board version is determined by U-Boot variable $board_id
which will be defined if a board ID has been burned on certain
OTP bits.
Use the value in this variable to create the $fdt_file variable
using the suffix "-id${board_id}" to point to the device tree
file that matches that board ID.

Signed-off-by: Hector Palacios <hector.palacios@digi.com>

https://jira.digi.com/browse/DEL-2160

meta-digi-arm/recipes-bsp/u-boot/u-boot-dey-2015.04/ccimx6/boot.txt

@@ -2,6 +2,12 @@
 # U-Boot bootscript for EMMC/SD images created by Yocto.
 #
 
+#
+# Set device tree filename depending on the board ID (if defined)
+#
+if test -n "${board_id}"; then
+	setenv fdt_file uImage-${soc_family}-ccimx6sbc-id${board_id}.dtb
+else
 	#
 	# Set device tree filename depending on the hardware variant
 	#
@@ -36,6 +42,7 @@ elif test "${module_variant}" = "0x13"; then
 	else
 		echo "------ Using default fdt_file"
 	fi
+fi
 
 # To detect if we are booting from SD card we get the UUID of the
 # boot partition and compare with the default one for the EMMC